Determining stress level based on the performance of the person in a game or puzzle

ABSTRACT

A system and a method are described for determining a stress level of a person based on the performance of the person in a game or puzzle. First, in a calibration phase the person is asked to judge his/her currently experienced stress level ( 120 ) and the person is asked to play ( 130 ) a game or puzzle resulting in a certain performance score. Subsequently in this calibration phase, the system links ( 150 ) the indicated stress level and the performance score. By repeating these steps a number of times, the system builds a table linking game performance scores and stress levels. The calibration phase will be executed initially and once every while to keep the system calibrated. Subsequently, in an operational phase, the person is occasionally asked ( 220 ) to play a game. Then, based on the current performance score and on the table assembled in the calibration phase, the system determines ( 250 ) the current stress level. Depending on the level, and on the period over which the level continues, the system may undertake some action ( 260 ), such as alerting the person or providing distraction.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a system, method and software fordetermining a stress level of a person.

2. Description of Related Art

Several surveys show that many people suffer from stress at work. Forexample, a survey by Northwestern National Life indicates that 40% ofworkers report that their job is very or extremely stressful. A surveyby Yale University indicates that 29% of workers report that they feelquite a bit or extremely stressed at work. According to Anderson et al,high stress yearly generates a cost of $136 per employee, making stressvery expensive for employers.

According to the National Institute for Occupational Safety and Health(NIOSH, see http://www.cdc.gov/niosh/stresswk.html), job stress can bedefined as the harmful physical and emotional responses that occur whenthe requirements of the job do not match the capabilities, resources, orneeds of the worker. Job stress can lead to poor health and even injury.Common complaints include loss of concentration, mood and sleepdisturbances, upset stomach, and headache.

An important way to reduce the costs of stress and to improve thewell-being of people at work is to detect in an early phase whether aperson has stress. When detecting stress in an early phase, measures canbe taken on time, such as solving stressful working conditions orhelping a person to cope with demanding job conditions.

Currently there are many ways to measure stress. A first known approachis to use self-report questionnaires. Still other known methods includeinterviews, or observations of a person, such as delayed reaction timesor heightened tendency to procrastinate. In a more advanced stage thenumber of mental or physical complaints can be counted in order todetermine the severity of these complaints.

According to other known approaches stress is determined by measuring aphysiological parameter of a person. For example, stress can be measuredby determining the level of the hormone cortisol in the blood. Cortisolis a corticosteroid hormone that is involved in the response to stress.

WO2006/105085 A2 discloses measuring a breathing pattern of a personwith a sensor and giving auditory or visual feedback corresponding tothe relaxation pattern of the person.

The mentioned approaches all have drawbacks for the person-under-test.First of all, he or she must explicitly do a test that is not a naturalpart of his or her daily life. According to some of the known approachesthe person is subjected to tests that only a professional can do. Insome cases this means that the person-under-test must even go to alaboratory or a professional infrastructure like a laboratory to besubjected to testing. Furthermore, at the time of performing the teststhe person may have suffered from stress for a longer time andcomplaints may have become severe enough to need actual professionalintervention.

It is an object of the invention to provide a system and method fordetermining the stress of a person that may be integrated in his or hernormal routine.

SUMMARY OF THE INVENTION

This and other objects of the invention are achieved by a systemaccording to claim 1, a method according to claim 14 and a computerprogram according to claim 15. Favorable embodiments are defined by thedependent claims 2-13 and 16-17.

According to an aspect of the invention a system is provided fordetermining a stress level of a person based on the performance of theperson in a game or puzzle. In a calibration phase the performance ofthe person in a game or puzzle is measured and information is storedlinking the performance to a given stress level of the person whenplaying the game or puzzle. Subsequently, in an operational phase, theperformance of the person in the game or puzzle is measured, again. Thestress level of the person is determined based on the measuredperformance and the information stored in the calibration phase.

The game-based test according to the invention is easier accessible to aperson than tests needing professional tools. By integrating the stresstest in a pleasant and normal activity like playing a game, people arelikely to be less disturbed. For this reason, the test results arelikely to better reflect a person's condition. Furthermore, playing agame not only is a means to detect the stress level, but at the sametime may help to reduce stress, to relax, to increase concentration, toreduce mental fatigue, and to make the person's memory function betteras is described in more detail in the co-pending patent application EP06124905.8. The invention can be applied in any environment where peoplesuffer from stress. It can be used at home, but also in the officeenvironment in order to detect and reduce stress and to improve themental health of workers. The game-based test according to the inventionpreferably is complementary to known tests that need professional tools.

Preferably, in the calibration phase the steps of measuring theperformance of the person in the game or puzzle and storing informationlinking the performance to a given stress level of the person areexecuted a plurality of times. For example, the calibration phase maylast for a month during which the person repeatedly plays games, forexample once a day. The system measures the person's performance at eachgame, and relates this to the given level of experienced stress of theperson. In this way the system can calculate the person's average gameperformance for each experienced stress level.

The system preferably is adapted for receiving an indication from theperson of the given stress level in the calibration phase. In this way,the given stress level is obtained in a very easy way without the needof any additional equipment.

Alternatively, the system is adapted for measuring the given stresslevel in the calibration phase. The given stress level may be measuredby measuring a physiological parameter of the person, which isindicative of stress, in a known way. Examples are the body temperatureor Galvanic Skin Response. Thereto the system needs to be provided withor connected to suitable sensors.

Preferably, the system is adapted for executing the calibration phaseinitially and repeating it, periodically. The calibration phase may berepeated every few weeks or months to keep track of learning andexperience effects.

According to an embodiment the system is adapted for performing anaction towards the person if the determined stress level in theoperation phase is high. Since, according to experts short-lived orinfrequent episodes of stress pose little risk, preferably the actiontowards the person is not performed in case of an incidental high stressmeasurement but only if the determined stress level in the operationphase is high over a period of time.

The action towards the person may be the generation of an alert for theperson. For example, the system may inform the person of the continuedhigh stress level and it may be suggested to take measures or to contacta professional for further tests or advise.

Alternatively, the action is providing distraction to the person. Thedistraction aims to relax the person. It may be inviting the person toplay a different game which is more relaxing than the game that is usedfor stress determination, to show relaxing pictures or to play relaxingmusic or to generate certain scents, etc.

For reasons of consistency in the operational phase the system isadapted for inviting the person to play the game or puzzle in time slotswith a similar activity level of the person. This is preferably a “lowstress” time slot because it is easier to detect a low performance in a“low stress” time slot than in a “high stress” time slot. The time slotswith similar activity level may be at a similar time of the day, forexample right after lunch.

The system may use known games to determine the stress or special gamesmay be designed for this purpose. According to a preferred embodimentthe game is a word memory game comprising neutral words and emotionalwords. Research has revealed that in a normal, i.e. non-stressedpopulation the emotional words should be recalled better. However, thisis not the case for people experiencing stress. They recall feweremotional words, whereas their performance on recall of neutral words isnot deterred. So, the person's performance in this game can be used todetermine his/her stress level.

According to an alternative embodiment the game is having the personnaming colors in which words are printed. The word list will be chosento include “neutral” as well as “highly relevant” words. These “highlyrelevant” words should be in the domain of the “work related stress”. Incase that the person is stressed the reaction times for naming the colorwill be longer for the highly relevant words.

According to a further aspect of the invention a method is provided fordetermining a stress level of a person based on the performance of theperson in a game or puzzle, comprising the following steps:

in a calibration phase: measuring the performance of the person in agame or puzzle and storing information linking the performance to agiven stress level of the person when playing the game or puzzle, and

in an operational phase, measuring the performance of the person in thegame or puzzle, again and determining the stress level of the personbased on the measured performance and the information stored in thecalibration phase.

Preferably, the method according to the invention is implemented bymeans of a computer program.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and its numerous objects andadvantages will become more apparent to those skilled in the art byreference to the following drawings, in conjunction with theaccompanying specification, in which:

FIG. 1 shows a flow chart of the steps that are executed during thecalibration phase in an embodiment of the system according to theinvention.

FIG. 2 shows a flow chart of the steps that are executed during theoperational phase in an embodiment of the system according to theinvention.

FIG. 3 shows an example of game performance as a function of time.

FIG. 4 shows a block diagram of an exemplary embodiment of the systemaccording to the invention.

Throughout the figures like reference numerals refer to like elements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Referring now to FIG. 1, the steps that are executed during thecalibration phase in an embodiment of the system according to theinvention will be described.

Before the system can determine a person's stress level via his/her gameperformance, it should be calibrated. This is due to the fact that everyperson performs differently under different levels of stress. A possibleway to calibrate is to let the person repeatedly play games over asufficiently long period of time, for example once a day during a monthand to let the user indicate the amount of stress experienced before thestart of each game. The system measures the person's performance at eachgame, and relates this to the amount of experienced stress as indicatedby the person. In this way the system can calculate the person's averagegame performance or score for each experienced stress level. Forexample, the person reaches an average score of 800 points in the “nostress” situation, 600 points at “medium stress”, and 400 points at“high stress”.

In order to calibrate the system, after the step of initialization 100,it is determined in step 110 if it is time to perform a calibrationmeasurement. If it is not, step 110 is repeated. If it is time for acalibration measurement, in step 120 the person is requested to indicatethe amount of stress experienced before starting to play the game. Forexample, the person may be prompted to indicate if he/she has no stress,medium stress or high stress. Alternatively, the level of stress may bemeasured by measuring a physiological parameter of the person, which isindicative of stress, in a known way. Examples are the body temperatureor Galvanic Skin Response. Thereto the system needs to be provided withor connected to suitable sensors.

Thereafter, in step 130 the person plays the game. In step 140 the gameperformance or score is determined. To enable the system the measuringof a person's stress level, various game performance indicators may beused. Depending on the game, the following performance indicators areuseful (but other indicators may be useful as well): the score (i.e.number of points) in a game

the time needed to complete a game

the level reached in a game

the number of errors made in a game

the number of objects (e.g. balls) that the person can deal withsimultaneously

the speed of objects (e.g. balls) that the person can deal with

the percentage of correct answers (in e.g. a crossword puzzle)

the time needed to start/enter/continue a game in a set of alternatinggames.

These performance indicators can be used both for calibrating thesystem, and for detecting stress in the subsequent operational phase,that will be described herein after.

In step 150 the measured performance is linked to the stress level thatthe person indicated in step 120 and both these parameters are stored.In step 160, the system checks if there are more calibrationmeasurements needed. If this is the case the system loops back to step110. If not, the calibration phase is finished in step 170. In this way,the system builds up a table linking game performance scores and stresslevels.

Once the system has been calibrated to a person, it can in a so calledoperational phase relate the performance of this person in a gamesession to his/her calculated average score for each experienced stresslevel. This is shown in FIG. 2.

After initialization (step 200) it is determined in step 210 if it istime to determine the stress level of the person. If this is the case,the system invites the person to play the same game that was playedduring the calibration phase. This game is played by the person in step220. After the game the person's performance is determined (step 230)and stored (step 240). In step 250 it is determined if an action shouldbe taken towards the person. If the performance stored in step 240correspond to medium or high stress for a longer period of time (e.g.during a week), the system determines that action should be taken. Anexample of such a situation is shown in FIG. 3. FIG. 3 shows theperformance (P) as a function of time (t). Area 310 (the highestperformances) corresponds to scores that were measured during thecalibration period when the person indicated that he/she had no stress.Area 320 corresponds to scores that were been measured during thecalibration period when the person indicated that he/she had mediumstress. Area 330 (the lowest performances) corresponds to scores thatwere measured during the calibration period when the person indicatedthat he/she had high stress. FIG. 3 shows 8 scores that were measured inthe operational phase, i.e. after the system was calibrated. The first 4scores in the upper area indicate that the person had no stress at thesemoments. However, the next 4 scores in the lower area suggest that theperson had high stress.

In step 260 the system may inform the person about his/her high stresslevel and may suggest to take measures or to contact a professional forfurther tests and advise. Note that the system need not inform theperson about an incidental performance that may indicate stress.Alternatively or additionally, in step 260 the system may providedistraction to the person. The distraction aims to relax the person. Forexample, the person may be invited to play a different game which ismore relaxing than the game that is used for stress determination, toshow relaxing pictures or to play relaxing music or to generate certainscents, as is described in more detail in the co-pending patentapplication EP 06124905.8.

In step 270 it is determined if calibration measurement(s) should berepeated. If this is the case, steps 120-160 of FIG. 1 are executed,again. If not, the system loops back to step 210. The calibration shouldbe repeated every few weeks or months in order to keep track of learningand experience effects.

According to experts and the National Institute for Occupational Safetyand Health (NIOSH), short-lived or infrequent episodes of stress poselittle risk. But when stressful situations go unresolved, the body iskept in a constant state of activation, which increases the rate of wearand tear to biological systems. It therefore appears sufficient toperform the test once a day. For reasons of consistency, it is preferredto play the game at the same moment and preferably in a ‘low stress’time-slot. For example, the person can be invited to play the game rightafter lunch or early in the morning when no meetings are planned. Thereason for this is that it is easier to detect a low score in alow-stress time-slot than in a high-stress time-slot.

The person's electronic calendar and/or to do list can be used by thesystem to determine the best time for both the calibration measurementsas well as the measurements during the operational phase. The samecalendars can also be used to find high stress times, which can beinterrupted by games to avoid build-up of stress.

Any type of game may be used in the system according to the presentinvention. However, it is preferred to use games derived from knownpsychological tests for the purpose of measuring stress. These gameswill be more resistant to factors of boredom or experience. A differenttype of game may be used to play in order to relax, have fun, andprovide a mental break from continued pressure.

Now, two examples will be described of games that are very suitable forthe stress determination according to the present invention Stresscauses impairments in memory retrieval. A game can be devised in whichpeople have to learn a list of words that they have to recall later thatday or the next day. This list of words can be set up such that itcontains neutral as well as emotional words (negative and positive).Neutral words could be words like window, forest, mountain, buildings,kangaroo, etc. So any word that is not related to the stressfulsituation. In case that the stressful situation is work, emotional wordscould be: traffic-jam, computer, deadline, presentation, report,meeting, stress, colleagues, lunch, coffee-break, etc. So any word thatreasonably is related to work. The human mind protects itself fromthreats by a number of mechanisms. One of the mechanisms is selectivememory. In case of remembering words, humans tend to block the wordsthat arouse negatively, like the emotional words, even when they mightbe positive like coffee-break or lunch. In a normal population theemotional words should be recalled better. However, this is not the casefor people experiencing stress. Fewer emotional words should berecalled, whereas performance on recall of neutral words should not bedeterred. See, for a more details on the relationship between stress andmemory retrieval “Impaired memory retrieval after psychosocial stress inhealthy young men (2005)” by. Kuhlmann, S., Piel, M. and Wolf, O. T.Journal of Neuroscience, 25(11). 2977-2982.

Reaction time measurements will reveal whether people are experiencingstress. There are many variants to the Stroop task, and there are a fewmechanisms by which it can work to expose people experiencing stress ornot. One such mechanism is the attentional bias. A Stroop task could beto have the person name the colors in which words are printed. The wordlist will be chosen to include “neutral” as well as “highly relevant”words. These “highly relevant” words should be in the domain of thepsychopathology, which in the present case is “work related stress”.When a person has a certain pathology, words related to that pathologymomentarily over-arouse that person. When somebody has overweight and istrying to lose weight, the word ‘diet’ is going to send a ‘rush’ throughhis/her body without that person being able to do anything about it.Similarly, when a person is stressed chronically, there will be certainwords that will send a surge through his/her mind and momentarily blockhim/her from doing anything else, such as naming a color. This can bemeasured by reaction-times (in milliseconds). So the same emotional(highly relevant) and neutral words as above can be used in this Strooptask. Only in this case the nature of the task will activate a differentmechanism. Reaction times for naming the color will be longer for highlyrelevant (emotional) words. For more information on Stroop tasks, see“The emotional Stroop task and psychopathology” (1996). Williams, J. M.G., Mathews, A., and MacLeod, C. Psychological Bulletin. 120(1), July1996, 3-24. More variations of the Stroop task can be devised. Thesetasks can be easily translated into a game-like format.

According to a preferred embodiment of the system the test isimplemented on a computer, such as a PC, Xbox, Playstation, mobilephone, PDA, etc. Since the test is personal, the computer should havemeans such that the person can identify him/herself or should be apersonal computer. FIG. 4 illustrates an exemplary computer system 400for implementing the steps according to FIG. 1. It shows a processor410, a memory 420, a display 430, an input means 440, which may be akeyboard and a mouse, and communication means 450. In this exemplaryembodiment the processor 410 executes instructions stored in the memory420, for executing the steps shown in FIGS. 1 and 2. The input means 440are used to control the game. The communication means 450 can be usedfor exchanging information with external systems (e.g. for adding newgames). The display 430 is used to show the game to the person, toinform the person about his/her game performance, and (if needed)suggest the person to take measures or to contact a professional forfurther tests and advise.

The invention can be resumed as follows: A system and a method fordetermining a stress level of a person based on the performance of theperson in a game or puzzle. First, in a calibration phase the person isasked to judge his/her currently experienced stress level and the personis asked to play a game or puzzle resulting in a certain performancescore. Subsequently in this calibration phase, the system links theindicated stress level and the performance score. By repeating thesesteps a number of times, the system builds a table linking gameperformance scores and stress levels. The calibration phase will beexecuted initially and once every while to keep the system calibrated.

Subsequently, in an operational phase, the person is occasionally askedto play the game. Then, based on the current performance score and onthe table assembled in the calibration phase, the system determines thecurrent stress level. Depending on the level, and on the period overwhich the level continues, the system may undertake some action, such asalerting the person or providing distraction.

As will be recognized by those skilled in the art, the innovativeconcepts described in the present application can be modified and variedover a wide range of applications.

Accordingly, the scope of patented subject matter should not be limitedto any of the specific exemplary teachings discussed, but is insteaddefined by the following claims.

Any reference signs in the claims shall not be construed as limiting thescope thereof.

1. System for determining a stress level of a person based on the performance of the person in a game or puzzle, wherein the system is adapted for: in a calibration phase: executing the steps of measuring (140) the performance of the person in a game or puzzle and storing (150) information linking the performance to a given stress level of the person when playing the game or puzzle, and in an operational phase, executing the steps of measuring (230) the performance of the person in the game or puzzle, again and determining (250) the stress level of the person based on the measured performance and the information stored in the calibration phase.
 2. System for determining a stress level according to claim 1, wherein the system is adapted for, in the calibration phase, executing the steps of measuring (140) the performance of the person in the game or puzzle and storing (150) information linking the performance to a given stress level of the person a plurality of times.
 3. System for determining a stress level according to claim 1, wherein the system is adapted for receiving (120) an indication of the person of the given stress level in the calibration phase.
 4. System for determining a stress level according to claim 1, wherein the system is adapted for measuring the given stress level in the calibration phase.
 5. System for determining a stress level according to claim 1, wherein the system is adapted for executing the calibration phase initially and repeating it, periodically.
 6. System for determining a stress level according to claim 1, wherein the system is adapted for performing (260) an action towards the person if the determined stress level in the operation phase is high.
 7. System for determining a stress level according to claim 6, wherein the system is adapted for performing (260) the action towards the person if the determined stress level in the operation phase is high over a period of time.
 8. System for determining a stress level according to claim 6, wherein the action is the generation of an alert.
 9. System for determining a stress level according to claim 6, wherein the action is providing distraction to the person.
 10. System for determining a stress level according to claim 1, wherein in the operational phase the system is adapted for inviting the person to play the game or puzzle in time slots with a similar activity level of the person.
 11. System for determining a stress level according to claim 10, wherein in the operational phase the system is adapted for inviting the person to play the game or puzzle at a similar time of the day.
 12. System for determining a stress level according to claim 1, wherein the game is a word memory game comprising neutral words and emotional words.
 13. System for determining a stress level according to claim 1, wherein the game is having the person naming colors in which words are printed.
 14. Method for determining a stress level of a person based on the performance of the person in a game or puzzle, comprising the following steps: in a calibration phase: measuring (140) the performance of the person in a game or puzzle and storing (150) information linking the performance to a given stress level of the person when playing the game or puzzle, and in an operational phase, measuring (230) the performance of the person in the game or puzzle, again and determining (250) the stress level of the person based on the measured performance and the information stored in the calibration phase.
 15. A computer program comprising computer program code means adapted to perform the steps of claim 14, when said program is run on a computer.
 16. A computer program as claimed in claim 15 embodied on a computer readable medium.
 17. A carrier medium carrying the computer program of claim
 15. 